This invention relates to coating printed sheets. It more particularly refers to a process and apparatus for coating sheets which have been printed on offset printing equipment.
In many applications it is desirable to apply a spot or overall coating to a printed sheet. For example, a UV curable or water-soluble polymer finish may be applied to a workpiece printed by offset lithography. The coating on the sheet is quickly dried while the surface of the ink is still tacky. This coating avoids the need for powder driers sprayed between sheets to present offsetting of oxidation-dried inks that are slow to dry. These coatings are also useful for providing a glossy finish that improves the rub-resistance of the workpiece and improves its overall appearance and feel. Finally, adhesive coatings may be applied to printed packaging; for example, heat-set adhesives may be applied to enable attachment of a feature such as clear plastic bubble of a package used to display the product. It is said that Ultraviolet cured and aqueous overprint coatings are, by some measurements, the fastest growing segments of the printing industry.
Application of coatings to a workpiece is made difficult by various requirements. For example, the coating should be uniform and its thickness should be controlled. Moreoever, the aqueous coating should be applied quickly, before its vehicle evaporates causing it to thicken. Finally, it is desirable for the coater to operate "in line" with the press that prints the workpiece to take full advantage of the fast drying capability of coatings and generally to simplify the manufacture of printed coated workpieces.
Butler U.S. Pat. No. 4,270,483 discloses an in line coating apparatus for attachment to a conventional offset lithographic printing press. The apparatus includes a set of rollers (i.e., pick-up roller 14 and application roller 16) to deliver coating material from a reservoir 18 to a standard press unit blanket roll 108. A metering rod 40 meters the amount of coating transferred to application roller 16.
An in line coater sold by Norton Burdett Co. of Nashua, N.H. has a single roller driven directly by a D.C. motor. The roller is a gravure cylinder that transfers coating to a standard press unit blanket cylinder. The coater is attached to a pivoting arm, and the unit can be pivoted away from the press unit when the coater is not in use.
Another in line coater, sold by IVT Colordry, Inc. of Fairfield, Conn., applies coating from a reservoir pan to a standard press unit blanket cylinder using a pick-up roller that delivers a coating supply to an applicator roller; the applicator roller applies the coating to the blanket cylinder of a press unit.
Kumpf U.S. Pat. No. 3,768,438 discloses a coater in which a fountain roller dips into a coating reservoir and transfers liquid coating material to a feed roller. The feed roller in turn transfers coating material to a coating roller that coats a sheet fed between the coating roller and a format roller.
Di Rico U.S. Pat. No. 4,685,414 discloses a process and apparatus for use in combination with an existing press unit wherein the coating means is retractable, to be used or not as the printer requires. In this device, the coating means utilizes the blanket roll of the last unit of the press, and this last unit cannot be used for color application means when it is used for coating. For example in a four color press, utilizing the coating apparatus of the '414 patent would then permit only three colors to be printed in in-line, single pass operation.
Bird U.S. Pat. No. 4,796,556 discloses an offset lithographic apparatus with a plate cylinder and a blanket cylinder, and an in line coater to apply liquid coatings either in a pattern or over the entire workpiece. The apparatus has a carriage which moves the coater between a first position operative association with the plate cylinder of the lithographic press unit (see full line of unit 72 in FIG. 1) and a second position in operative association with the blanket cylinder of the lithographic press unit (see broken line of unit 72 in FIG. 1). In the first position the coater applies spot coating, and in the second position the coater applies coating over the entire sheet.
Satterwhite U.S. Pat No. 4,308,796 discloses apparatus for adapting an offset lithographic press to flexographic operations, the flexographic operation being either for coating or printing. Coating is achieved by applying a photosensitive plate to the lithographic blanket roll of the offset press. A transfer roll supplies coating to the plate. Inking is achieved in a like manner but with a flexographic plate having raised image areas.
Makosch U.S. Pat. No. 4,397,237 discloses a pivoting secondary inking system ("B" in FIG. 2).
Preuss et al. U.S. Pat. No. 3,391,791 discloses a sheet coater which moves into engagement with various cylinders in a press delivery area.
Knodel et al. U.S. Pat. No. 3,916,824 discloses a coating assembly which includes a fountain roll, a metering roll and an applicator roll for coating band of ribbon material. The coater is horizontally displaceable on an auxiliary frame.
Jahn U.S. Pat. Nos. 4,615,293 and 4,706,601 disclose separate duplex coating units disposed downstream of a printing press. The units permit coating of selected portions of the workpiece using a relief plate or permit blanket coating.
Switall U.S. Pat. No. 4,617,865 discloses a coater that can be pivoted into and out of position in contact with the blanket cylinder of the press unit; the coater being retractable with the same limits as that of the Di Rico device, i.e., the coating and printing functions cannot be performed simultaneously.
Jirousek U.S. Pat. No. 2,320,523 discloses a self-adjusting dampening roll.
Edwards U.S. Pat. No. 4,222,325 discloses a retractable dampening and inking unit.
Egnaczak U.S. Pat. 3,800,743 discloses a coater for a photoelectrophoretic process.
DeLigt U.S. Pat. No. 3,397,675 discloses a coating or printing station having its applicator and transfer rolls attached to pivotally mounted supporting frames.
Some commercial presses, such as Heidelberg GTO and MO include an extra blanket cylinder e.g., for numbering, printing extra colors, perforating, center slitting, etc. This added cylinder is a fixed part of the press, and does not retract with associated equipment for numbering or imprinting.